1. Field of the Invention
This invention pertains to novel organic gels and to their uses. In particular, this invention pertains to organic gels of non-polar liquid organic solvents (e.g. perchlorinated alphatic hydrocarbons of one to two carbon atoms, such as perchloroethylene). This invention also pertains to the use of such organic gels as gelled pigs in pipeline cleaning.
2. Description of the Prior Art
Pipeline efficiency in volume can be lost by scale buildup in the interior lining of the pipe. Mechanical pigs and/or gelled chemical pigs have been used to remove scale. The mechanical pigs are normally solid bullet-shaped devices which have wire brushes or abrasive surfaces to physically abrade the scale interior of the pipe. The gelled chemical pigs on the other hand, remove the surface deposits by dissolution and/or by picking up loose debris as they pass through the pipeline. Purinton described a variety of aqueous gels which were useful in pipeline cleaning in Ser. No. 241,962 filed Mar. 9, 1981. The disclosure of this patent application is incorporated herewith by reference.
Scott described a method for cleaning pipeline using an aqueous gel of a different type in U.S. Pat. No. 4,216,026. Scott alleges that plugs of Bingham plastic fluids are effective in picking up loose debris and minor amounts of liquids as the plug moves through the pipeline. The plug is used in combination with mechanical scrapers.
Jagger et al. also described a method of removing fluids and solids from a pipeline in U.S. Pat. No. 4,003,393 using an organic liquid gel with a metal salt of an aliphatic ester of orthophosphoric acid.
While the aforementioned aqueous gels have many desirable properties, certain types of scale or scale components are effectively removed only by an organic solvent. In most instances, a "fill and soak" type treatment with a liquid solvent is not practical due to the volume of solvent required. Waste disposal of such a large volume of material is also a commercial problem. Applicant conceived that these problems could be solved by a gelled organic pig if a gel of suitable stability could be found.
There are, of course, many organic gels described in the literature. For example, in U.S. Pat. No. 3,505,374 Monroe described the use of magnetite salts of alkyl oleyl orthophosphate as gelling agents for hydrocarbons and halogenated hydrocarbon liquids. Crawford et al. (U.S. Pat. No. 3,757,864) taught that the pressure drop of a confined non-polar organic liquid in motion due to friction is lessened by admixing with the liquid one or more aluminum salts of an aliphatic orthophosphate ester. Crawford et al. also taught that such esters can gel the liquids. Dickerson (U.S. Pat. No. 3,219,619) thickened hydrocarbons with t-butylstyrene interpolymers containing metal carboxylate groups. Haigh et al. (U.S. Pat. No. 3,527,582) formed reversible gels of liquid hydrocarbons using a crosslinked latex polymer of an alkyl styrene. But, as Monroe illustrates, thickened organic fluids are not the same as organic gels. With organic gels, the gel consistency will not disappear on dissolution of the gel. With sufficient dissolution, the solvent swollen gelling agent will appear as a distinct phase in suspension. Moreover, the gel structure has a viscosity profile that is quite different from liquids that are merely thickened but not gelled. If a gel is to be used as a pipeline pig, the rheology and chemical and physical properties of the gel must meet certain demands. For example, the gel must be viscoelastic and self-sustaining so that it will not break up as it is being forced through the line under pressure. It is also desirable for the gel to have the capacity to retain suspended solids and the ability to sustain a gel/liquid interface. This later capability is needed because in many instances it is desirable to displace with the gelled pig and/or to drive the pig directly with a liquid under pressure. Also, it is desirable in many instances to use a pig train which will have one or more chemical pig segments and the gel desirably would have a gel structure that would prohibit or substantially inhibit comingling of liquids in front of and/or behind the gelled pig (sometimes called fluid by-pass).